386 THE SEED Atft) ITS GERMINATION 



But the withdrawal of the process of fertilisation to 

 the interior of the well-protected ovule has another great 

 advantage it enables the zygote, the result of fertilisa- 

 tion, to be developed into an embryo in a protected 

 position, and to be supplied by the parent plant with 

 the food necessary to its development in that position. 

 In this way the young plant is able to establish itself 

 in a short time after the seed germinates -it has a 

 chance of penetrating quickly into the damp soil below 

 the surface because it has a store of food at its disposal 

 for rapid growth. 



In the fern plant the sexual generation is a free- 

 living green plant produced by the germination of the 

 spore on the soil. The young sporophyte is " parasitic " 

 on the prothallus during the first stage of its growth. 

 In the seed plant the prothallus is reduced to its lowest 

 terms and is " parasitic " on, or rather in, the mother 

 sporophyte (the " vegetative " plant). But not only so : 

 the new sporophyte produced from the zygote is also 

 parasitic on (i.e. it derives its food from) the mother 

 sporophyte, and is protected by it in the altered 

 megasporagium (seed) up to a certain stage of its 

 development, when it can, on the germination of the 

 seed, rapidly become free living. 



Thus the seed plant has successfully solved the problem 

 of sexual reproduction, and of giving the new generation 

 a good start in life under conditions which the lower 

 plants are quite unable to meet. The principle of the 

 mating of the delicate and easily destroyed gametes 

 inside the body of the parent, and of the protection of 

 the embryo during the^ early stages of its life, is the 

 same that we see successful in the higher animals, 

 though the details of the mechanism are so widely 

 different. Taken together with the power of maintain- 



